It's whatever you need. If you're just running a simple web-app that doesn't need to do much processing, get something small. If you want to run a database and

It's whatever you need. If you're just running a simple web-app that doesn't need to do much processing, get something small. If you want to run a database and have a lot of IO, you'll need something beefier. There is no single "best" size. Get what fits your needs.